1. Field of Invention
This invention relates to dental matrix bands and, more particularly, to improvements in such matrix bands by which the full vertical surface contour of a tooth may be accurately complemented by a mold surface so that the exterior surface of a filling compacted against such mold surface will be a smooth continuation of or lie flush with the original surface contour of the tooth.
2. Description of the Prior Art
Matrix bands are extensively used by dentists to fill cavitations which open through any of the vertical surfaces of a tooth. Such bands are applied circumferentially about the crown of a tooth with the lateral dimension or width of the band extending from the cervical toward the occlusal surfaces of the tooth. Once in place, the band is placed under hoop stressing by a retaining appliance to provide a dam-like mold against which a filling material may be compacted. Conventional matrix bands as well as retaining appliances incident to their use are represented by the disclosures of U.S. Pat. Nos. 2,502,903; 2,538,486; 2,591,744; and 3,305,928, all issued to the inventor, B. F. Tofflemire.
Tofflemire-type matrix bands are formed of thin, foil-like metal having the characteristics of stainless steel and are shaped with an arcuate central portion merging tangentially with two linear arms capable of cooperation with the hoop stressing retainer appliance. When applied about a tooth crown, the arcuate central portion assumes a frusto-conical configuration conforming generally to the divergence of crown surfaces from the cervical. The frusto-conical shape of the placed matrix band insures a peripheral seal of the band at the cervical and is effective for compaction of filling material in fillings opening through surfaces at the mesial or front and distal or rear quadrants of a tooth crown. Cavities which open through lateral quadrants (lingual and facial surfaces) of the tooth, however, are not closed by the inner matrix band surfaces with the result that difficulty is encountered in the placement and compaction of filling material in such cavities.
The effectiveness of existing Tofflemire-type matrix bands in filling cavities which open to the mesial or distal surfaces of teeth is due in part because of the relatively predictable contour of these surfaces and also in part because of the availability of an adjacent tooth to act as a support for a wedge or pry by which the matrix band may be deflected against the tooth being filled. Surfaces on the lingual or facial sides of a tooth, however, are not only of more widely varying contour, but also are often reentrant as in the case of molars. In such cases, the hoop tension in the applied matrix band acts to hold the band spaced away from the concave reentrant portions of the exterior tooth surfaces to a point where it is difficult, if not impossible, to achieve the degree of compaction necessary at the original surface contour of the tooth. Attempts have been made at solutions to this problem by providing a matrix band with a preformed concavity (U.S. Pat. No. 3,842,505--Wilmer B. Eames) or by retainers for compressing the matrix band against the tooth exterior (U.S. Pat. No. 2,646,622--D. R. Christy et al.). Such approaches to the problem, however, have not been totally satisfactory due to the difficulty of accommodating varying contours as in the case of the preformed matrix band or by a compromise in the availability of hoop tensioning. It is apparent, therefore, that improvements are needed in dental matrix bands to achieve a complementary mold surface for the complete exterior crown surfaces of a tooth.